MONOBROMACETIC ACID PREPARATION 18. Monobromacetic Acid, CH2Br.COOH. Hell, Bcr.) 1881, 14, 891 ; Volhard, Annalen, 1887, 242, 141 ; Zelinsky, Ber., 1887, 20, 2026. 30 grms. (30 c.c.) glacial acetic acid. I05 3) (35 c.c.) bromine. 5 „ red phosphorus. All the above substances must be dry. The acetic acid is frozen in ice, and any liquid drained off, and the red phosphorus is washed with water to free it from phosphoric acid, dried in the steam oven, and kept over sulphuric acid in a desiccator until required. The bromine is placed in a separating funnel with half its volume of concentrated sulphuric acid overnight, and then separated. The apparatus is shown in Fig- 63 . It consists of a round flask (250 c.c.) attached to an upright condenser, which is provided with a cork. A tap-funnel con- taining the bromine passes through one hole, and a wide bent tube, attached at its lower end to a funnel, passes through the other. As a large quantity of hydrobromic acid is evolved in the reaction, the funnel is made to touch the surface of water contained in a beaker, whereby it is completely absorbed. The phosphorus and acetic acid are placed in the flask, and bromine dropped in from the tap-funnel.* A vigorous reaction occurs, and the liquid becomes very warm. After half the bromine has been added the action moderates, and the remainder may be run in more quickly. When the whole has been added, the liquid is boiled gently until the colour of the bromine disappears. It is now allowed to cool, and the liquid decanted into a distilling flask for distillation in vacua. Care must be taken not to touch the substance with the hands, as even a small quantity produces very unpleasant sores. The apparatus for distilling in vacua is shown in Fig. 56 (p. 85). FIG. 63.